Q: What’s the difference between those new four-strain vaccines and the regular kind?

A: For more than 30 years, the vaccine has offered protection against three influenza strains — two common Type A strains called H1N1 and H3N2, and one strain of Type B. Flu strains continually evolve, and the recipe for each year’s vaccine includes the subtypes of those strains that experts consider most likely to cause illness that winter.

Type A flu causes more serious disease and deaths, especially the H3N2 form that made last year such a nasty flu season. But the milder Type B flu does sicken people every year as well, and can kill. Two distinct Type B families circulate the globe, making it difficult to know which to include in each year’s vaccine. Adding both solves the guesswork, and a CDC model estimates it could prevent as many as 485 deaths a year depending on how much Type B flu is spreading.

Q: How can I tell if I’m getting the four-strain vaccine?

A: All of the nasal spray version sold in the U.S. this year will be this new variety, called FluMist Quadrivalent. The catch is that the nasal vaccine is only for healthy people ages 2 to 49 who aren’t pregnant.

If you prefer a flu shot, ask the doctor or pharmacist if the four-strain kind is available. Younger children, older adults, pregnant women and people with chronic health conditions all can use flu shots. Four-strain versions are sold under the names Fluzone Quadrivalent, Fluarix Quadrivalent and FluLaval Quadrivalent.

Manufacturers anticipate producing between 135 million and 139 million doses of flu vaccine this year. Only about 30 million doses will offer the four-strain protection.

Q: Who should seek it?

A: Type B flu tends to strike children more than the middle-aged, Poland noted. And he said it’s not a bad idea for seniors, who are more vulnerable to influenza in general. But the CDC doesn’t recommend one vaccine variety over another, and the American Academy of Pediatrics said either kind is fine — just get vaccinated.

Q: How are these new vaccines different from the high-dose flu shot for seniors?

A: Fluzone High-Dose protects against the traditional three strains of flu, but it quadruples the standard vaccine dose in an effort to rev up age-weakened immune systems don’t respond as actively to regular flu shots.

The government calls the high-dose shot an option for seniors, not one that’s proved better. Last week, Sanofi Pasteur said initial results from a study of 30,000 seniors vaccinated over the past two flu seasons suggest the high-dose shot is about 24 percent more effective. Federal health officials will have to review the full study results to see if they agree.

Q: What if I’m allergic to eggs?

A: Traditional flu vaccine is made from viruses grown in eggs, and specialists say it’s usually not a problem unless someone has a serious egg allergy. But the new FluBlok vaccine eliminates that concern because it is made with cell technology, like many other nonflu vaccines. So far, it’s only for use in people ages 18 to 49.

Q: What if I’m scared of needles?

A: If you don’t qualify for the ouchless nasal spray vaccine, there is one shot made with a teeny-tiny needle that pricks the skin instead of muscle. Called Fluzone Intradermal, it’s available for 18- to 64-year-olds, and protects against the usual three strains.

Q: How soon should I be vaccinated?

A: Early fall is ideal, as it’s impossible to predict when flu will start spreading and it takes about two weeks for protection to kick in. But later isn’t too late; flu season typically peaks in January or February.

Q: How much does flu vaccine cost?

A: The vaccine is covered by insurance, and Medicare and some plans don’t require a co-pay. Drugstore vaccination programs tend to charge about $30; expect the quadrivalent versions to be slightly more expensive.